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3. Gundersen LCS, Reimer GM, Wiggs CR, Rice CA. Map showing radon potential of rocks and soils in Montgomery County, Maryland (1:62 500). U.S. Geol. Surv., Miscellaneous Field Studies Map MF-2043, 1988.
4. The relationship between indoor radon and data from regional risk maps in the eastern Bohemian districts, Czech Republic;Hulka,1994
5. Towards a classification of radon prone areas in Germany;Kemski,1994